Equipment for delivering liquid, particularly oil burners

ABSTRACT

The invention relates to an oil pump unit for oil burners which includes a known assembly of a geared pump, a sump at a lower level, and a pressure regulator valve. Air vent means are provided which includes apparatus for feeding back to the pump pressurized liquid from the pressure regulator. The pump proper has novel passage means for receiving the fed back pressurized liquid to the pumping chambers to effect a venting of pressurized air from the chambers.

United States Patent Petersen et a1.

[ EQUIPMENT FOR DELIVERING LIQUID, PARTICULARLY OIL BURNERS [72] lnventors: Jorgen Hartvig Petersen; Gunnar Lyshoj Hansen, both of Nordborg, Denmark [73] Assignee: Danfoss A/S, Nordborg, Denmark [22] Filed: Dec. 2, 1969 [21] Appl. No.: 881,437

[52] U.S.Cl ..4l7/304,417/310,417/435, 418/171, 418/180 [51] 1nt.(31. ..F04b 49/00, FOlc 1/10, F04c 1/06 [58] Field of Search ..4l7/296, 300, 302, 303, 304, 417/307, 308, 310, 31 1, 435; 418/171, 180

[56] References Cited UNITED STATES PATENTS 2,915,015 12/1959 Erikson et al ..417/303 3,025,802 3/1962 Browne ..418/82 3,237,566 3/1966 Roenick... ..418/171 3,322,134 5/1967 Enemark ..4l7/310 3,356,032 12/1967 Roeske ,413/180 3,385,220 5/1968 Dymond .417/300 3,446,231 5/1969 Magnusson .417/308 Primary Examiner-Carlton R. Croyle Assistant Examiner-John .1. Vrablik Attorney- Wayne B. Easton [5 7] ABSTRACT The invention relates to an oil pump unit for oil burners which includes a known assembly of a geared pump, a sump at a lower level, and a pressure regulator valve. Air vent means are provided which includes apparatus for feeding back to the pump pressurized liquid from the pressure regulator. The pump proper has novel passage means. for receiving the fed back pressurized liquid to the pumping chambers to effect a venting of pressurized air from the chambers.

2 Claims, 5 Drawing Figures Pmmsnmmrsza 3535604 SHEET 1 OF 2 Fig 1 EQUIPMENT FOR DELIVERING LIQUID, PARTICULARLY OIL BURNERS The invention relates to equipment for delivering liquid, particularly to oil-bumers, and incorporating a geared pump which draws liquid from a sump disposed at a lower level and passes it to a consumer unit by way of a regulator which keeps the pressure constant and is provided with a return pipe.

In installations of this kind, operating on the two-line system, there is a danger that the pump may draw air, together with the oil, from the sump disposed at a lower level. The occluded air leads to the development of considerable noise in the geared pump and to cavitation phenomena. Also, larger amounts of occluded air adversely affect the operation of the regulator fitted at the output side, and, in particular, the proper functioning of a cutoff valve such as is required in the case of oil-burners. Experience has shown that present delivery equipment can deal with occluded air up to a maximum of 3 cm.. However, in the case of a large suction lift, e.g., up to 15 m., considerably greater amounts of occluded air, e.g., up to cms", may occur.

Centrifugal air-separators are known which are fitted at the output side of the pump. These, however, require-a considerable amount of space, but nevertheless cannot eliminate the noise and cavitation phenomena occurring in the pump.

Proposals have also been made for diverting the air, delivered during the startup period of the pump, along a path which is rendered ineffective after the pump begins to operate at full speed. It is not however possible thereby to remove the disadvantageous effects which are caused by the occluded air occurring during operation.

It is also known to incorporate in the return pipe anonreturn valve which opens in the direction of the discharged liquid and which is intended to prevent oil being sucked up through the return pipe. The restoring forces of this valve are very small.

The object of the invention is to provide equipment for the delivery of liquid of the initially described kind in which the problems associated with occluded air can be completely or for the most part overcome.

in accordance with a first basic idea of the invention, this object is achieved by providing the geared pump, in the area of its greatest chamber volume between the suction and pressure sides and preferably in the plane of symmetry of the geared pump, with a feed device, which provides the chambers with liquid under a filling pressure which is substantially higher than atmospheric pressure, but is still considerably below the operating pressure of the delivery equipment.

In this arrangement, each chamber, during its passage from the suction side to the pressure side, is subjected through the feed device to a pressure which is considerably greater than atmospheric pressure. if the chamber contains air, liquid under this pressure is fed in again and the air is correspondingly compressed. The volume of air is thus reduced upon reaching the pressure side. The compression still possible at this point is correspondingly small with the result that the noise, cavitation phenomena and instability of the delivery pressure are negligibly small.

In order to achieve the desired effects, the pressure of the liquid that is fed in should be in excess of 2 atmospheres excess pressure. The optimum value depends upon the operating pressure of the delivery equipment. In the case of oil-pumps having an operating pressure of 7-15 atmospheres excess pressure, the filling pressure should be 5 atmospheres excess pressure and above.

A particularly simple arrangement for producing the filling pressure consists in providing in the return pipe a valve which opens in the direction of the discharged liquids and which only opens at a return pressure equal to the filling pressure of the feed device, and in connecting the feed device with the return pipe at a point ahead of this valve. This valve does not interfere with the normal return operation, but maintains, in the return pipe, a pressure which can be used as the filling pressure.

In those cases in which air is to be cleared by way of the return pipe when the pump starts up. it is advantageous to bypass the valve in the return pipe by means of a throttle passage which offers high resistance to the liquid but little resistance to air. For example, the throttle channel can take the form of a groove in the surface separating the valve seat and the closure member. Air that has a troublesome effect during startup can be cleared through this throttle passage; nevertheless the valve only opens if the return pressure, prescribed in accordance with the invention, obtains :in the return pipe.

Particularly advantageous is the provision of a second feed device which, in the form of a throttle gap, extends from the pressure side towards the first feed device, thereby overlapping at least one chamber. This second feed device, communicating with the pressure side, leads to a gradual rise in pressure in the chamber moving from the first feed device to the pressure side, this rise resulting from the throttling action. Consequently, any air present, already compressed because of the first feed device, is continuously funther compressed to the delivery pressure, oil being fed in again from the pressure side by way of the throttle gap. Consequently, when the pressure side is reached, no changes in pressure and volume due to the occluded air occur at all, so that no noise and cavitation effects or pressure fluctuations are likely either.

The throttle gap of the second feed device can be connected with the first feed device. There then occurs along this throttle gap a drop in pressure which is equal to the difference between the delivery pressure and the filling pressure to the first feed device. The end of the throttle gap can also be connected to the return pipe behind the valve by way of a blocking member, e.g., a closing valve or a throttle point offering high resistance to the liquid, but little resistance to air. With the help of the throttle point and of the cross-sectional dimension of the throttle gap, adjustment to give the required pressure-drop can be made independently of the first feed device. Furthermore, the connection to the blocking member bypasses the valve in the return pipe, so that air can escape freely upon startup.

The proposal of the invention is particularly advantageous if the gear set consists in known manner of a toothed wheel and an internally toothed ring which surrounds it and has one tooth more, the wheel and the ring rotating about their mutually offset axes. According to the invention, this very simple pump construction can be used for considerably greater suction lifts than heretofore. Occluded air of up to 20 cm. can be dealt with without the occurrence of troublesome noise.

In this connection it is expedient for the supply and discharge passages on the pressure and suction sides to overlap several chambers but at a distance of at least one chamber ahead of the first feed device. All danger of a short circuit is eliminated by the distance provided. Furthermore, there occurs between the first feed device and the pressure side a compression of the chamber contents so that any air present is still further compressed. If the chamber should have been completely filled with liquid, the surplus can be discharged through the throttle gap of the second fe-ed device.

As already mentioned, difficulties occur with the cutoff valve and the pressure-regulating means as a result of air being occluded. In accordance with a second aspect of the invention and employing the same basic idea, these difficulties can be overcome entirely or to a large extent by combining the regulator for keeping the pressure constant, in known manner, with a cutoff valve which closes when the pressure or the amount of the liquid supplied falls below a prescribed limiting valve, and by fitting, in the return pipe, a valve which opens in the direction of the discharged surplus liquid and which holds the pressure in the return pipe at a value considerably above atmospheric pressure.

Previously, when occluded air had reached the regulator, the air flowed away preferentially through the throttle gap of the regulator into the return pipe. If the discharge of air took place faster than the replacement of liquid by the pump, a pressure-drop occurred which caused undesired closing of the cutoff valve. However, if in accordance with the invention, provision is made for the air not to be able to escape so rapidly into the return pipe, under otherwise like conditions, there is no difficulty as regards the pump supplying further fluid sufficient to maintain the required pressure.

This step is of advantage particularly in the case of sensitive cutoff valves that are intended to close very rapidly, for example if the pump speed has diminished by only l-20 percent. A sensitive valve of this kind preferably incorporates the feature that a cutoff valve closure piston is connected to a moving part of a restrictor and is also adjustable by means of a regulating piston which is acted upon by the pressure drop at the restrictor and by a spring, and regulates the quantity returned.

The steps for combatting the disadvantageous consequences of occluded air can of course be combined, the higher pressure in the return pipe being used both for refilling with the help of the first feed device and for the slow discharge of air from the combined regulating and cutoff means.

The invention will now be described in more detail by reference to an embodiment illustrated in the drawing, in which:

FIG. 1 is a diagram showing how the delivery equipment of the invention is connected up,

FIG. 2 is a schematic cross section through the geared pump incorporating the feed devices of the invention,

FIG. 3 is a section through that part of the return pipe containing the valve,

FIG. 4 is a cross section on the line A-A of FIG. 3, and

FIG. 5 is a longitudinal section through the combined pressure regulating and cutoff means shown in FIG. 1.

As shown in FIG. 1, a pump 1 draws oil from a sump 2, disposed at a lower level, by way of a long suction pipe 3 and passes the oil through a pressure pipe 4 to a combined pressure regulating and cutoff means 5, from which there runs a pipe 6, supplying a consumer unit, here, the nozzle 7 of an oilburner, and a return pipe 8 extending to the sump 2. The quantity of oil returned to the tank 2 through the return pipe 8 is such that the pressure in the supply pipe 6 remains approximately constant. The return pipe contains a valve 9 which only opens when the pressure obtaining in the return pipe 8 is above 2 atmospheres excess pressure, preferably 5 atmosphere excess pressure. Consequently, the return pipe 8 has a portion a of higher pressure and a portion b of lower pressure. A filling pipe 10, the purpose of which will be described later, branches from the part a.

A case 1] contains a circular opening 12 in which a toothed ring 13 having nine teeth 14 rotates about its axis M Mounted on a driving shaft 15 is a toothed wheel 16 having eight teeth 17, this wheel rotating about its axis M Displacement chambers 18 are formed between the teeth ofthe ring 13 and the wheel 16. In the sidewall on the suction side is a crescent-shaped passage 19, which communicates with the suction pipe 13. On the pressure side in the sidewall is a crescent-shaped passage 20, which communicates with the pressure pipe 4. The filling pipe 10 leads to a first feed device 21 in the form of an elongate groove which extends in that plane of symmetry of the pump running through the axes M and M, of the toothed ring and toothed wheel. The feed device 21 overlaps the chambers 18 that move from the suction side to the pressure side and therefore connect them to the filling pipe 10. Furthermore, there extends from the passage on the pressure side a second feed device 22 in the form of a throttle gap, that is to say a very shallow recess, running to the first feed device 21. This second feed device 22 overlaps the chamber moving from the plane of symmetry to the pressure side. At that of its ends remote from the pressure side, the second feed device 22 is likewise in communication with the filling pipe 10.

As shown in FIGS. 3 and 4, there is provided in the case 11 an insert 23, the end-face of which forms the seat 24 of the valve 9 and through which runs the portion 8a of the return pipe. A closure member 26, which only opens when the pressure in the portion 8a has exceeded a predetermined value, is

pressed against the seat 24 by means of a spring 25. The adjacent bore 27 leads to portion 8b of the return pipe. The closure member 26 contains a throttle passage 28, which, in plan view, has the shape shown in FIG. 4. This throttle passage offers high resistance to oil but very small resistance to air.

The equipment so far described operates as follows:

The chambers 18 of the pump 1, increasing in size on the suction side, accept oil from the suction-side passage 19 as a result of their expansion, and when they diminish in size pass it to the pressure-side passage 20 and thus to the pressure pipe 4. A delivery pressure is created by the resisting elements, particularly the nozzle 7, arranged on the output side. With the help of the means 5, this delivery pressure is kept constant, for example at a pressure of IO atmospheres excess pressure. The valve 9 in the return pipe 8 is opened to an extent such that a pressure of e.g., 5 atmospheres excess pressure is set up in portion a of the pipe 8 and therefore in the filling pipe 10.

The same pressure of 5 atmospheres excess pressure is therefore also present in the area of the first feed device 21. In the second feed device 22 a pressure-drop of 10 to 5 atmospheres excess pressure occurs in the direction opposite that in which the toothed wheel 16 rotates. If the chambers 18 now do not merely contain oil but air as well, this air, upon reaching the first feed device 21, is subjected to the increased pressure of 5 atmospheres excess pressure and is therefore compressed. The corresponding volume is refilled with oil from the filling pipe 10 (solid-line arrow). When the chamber continues to move towards the pressure side, it reaches zones of gradually increasing pressure, because of the second feed device 22, so that the occluded air is always further compressed until, upon reaching the passage 20, it is compressed to an extent corresponding to the full delivery pressure. During this compression, oil can still be filled into the chamber 18 again from the pressure-side passage 20 through the device 22.

The suction-side passage 19 terminates at a distance equal to approximately one chamber before the first feed device 21; approximately the same distance is provided between this device 21 and the pressure-side passage 20. The changes in the volume of the chamber 18 occurring during the passage over this distance are permissible since the chambers are not only filled through the filling pipe 10, but if required can also be relieved of pressure (broken-line arrow). Oil which flows through the second feed device 22, but is not required for filling the chambers 18, or which is still expelled from a chamber 18 after moving past the first feed device 21, but before reaching the passage 20, can also be discharged in the direction of the arrow.

If, when the pump starts up, insufficient pressure has built up on account of there being too much air in the suction pipe 3 of the pump, the valve 9 remains closed. The air delivered by the pump can however be discharged by way of the first feed device 21, possibly in conjunction with the second feed device 22, through the filling pipe 10 into the return pipe 8, and from there can pass into the atmosphere through the throttle gap 28 in the valve 9. Consequently, even the large quantities of air present upon startup cause no problem.

The second feed device 22 does not need to communicate with the filling passage 10. It can for example be provided on that side of the gear set opposite the filling device 21 and can communicate with the part b of the return pipe 18, not under pressure, through a passage 29, shown in dash-dot lines, thereby circumventing the valve 9. This passage 29 contains either a throttle, which offers very high resistance to the oil but little resistance to air, or a shutoff valve which closes when top gearset operating speed is reached.

FIG. 5 shows a form of construction of a pressure regulating and cutoff unit used in accordance with the invention.

The case 11 has a cylindrical bore 30 in the wall of which is the mouth 31 of a bore 32 for the pressure pipe 4, the mouth 33 of a bore 34 for the return pipe 8 and the mouth 35 of a bore 36 for oil flowing back to the suction side of the pump. A further bore 37 is connected to the suction side for the purpose of relaxing pressure. One end of the bore 30 is closed by an insert 38 which forms part of the delivery pipe 6 and the seat of a cutoff valve 39 which will be described in more detail below. An adjusting piston 40 and a regulating piston 41 having the same outside diameter are displaceable in the cylindrical bore 31). The regulating piston 41 surrounds the closure piston 42, which is linked to the regulating piston 41 to give approximately synchronous movement.

At one end the adjusting piston 40 is under pressure from the liquid contained in the chamber 43 and at the other end under pressure from a rated spring 44 which is supported on an adjustable backing member 45. The adjusting piston 40 has an extension in the form of a hollow cylinder 46, and on the resultant shoulder 47 there bear a sealing washer 48, containing a central hole 49, and a backing disc 50, which are pressed by the rated spring 44 on to the shoulder, so that a transverse floor is provided in the adjusting piston 40. In operation, the adjusting piston 40 occupies a position determined by the magnitude of the supply pressure and the setting of the rated spring 44. The closure piston 42 constitutes a closure member 51 at one end, and, at the opposite end, a cylinder 52 which is inserted in the hollow cylinder 46. The closure member contains transverse and longitudinal bores 54 and 55, through which the chamber 43 can communicate with a chamber 56 on the opposite side of the regulating piston 41. To make manufacture simpler, the longitudinal bore 54 is closed by a ball 57, so that a recess 58 remains in the closure member 51. The end edge 59 of the hollow cylinder 46, together with the mouth 60 of the transverse bore 53, forms a cutoff valve in the illustrated nonoperating position and a restrictor in normal operation when the adjusting piston 40 has moved to the right. Between the cylinder 52 and the sealing washer 48 is a bottom chamber 61, the volume of which is zero in the illustrated nonoperating position, since the sealing washer 48 bears against the end-face of the cylinder (the chamber 61 being drawn larger only for the sake of greater clarity). When the size of this bottom chamber 61 changes, oil is supplied through the clearance between piston 52 and cylinder 62, acting as a throttle, from an annular groove 63, which communicates with the mouth 60, or the oil is discharged into said annular groove. The oil cushion ensures that the closure piston 42 participates in the rapid movements of the adjusting piston 40, but permits slow relative movement between these two parts.

The regulating piston 41 is subjected at one end to the pressure in the chamber 43 and, at the other end, to the pressure in the chamber 56 and the force of a differential-pressure spring 64. The differential pressure is produced by the pressure drop at the restrictor 59, 60. Consequently, the piston 41 occupies a position such that its end-edge 65 exposes a certain cross section of the mouths 33 and 35. The regulating piston 41 has a wall 66 which is of considerable axial length and which overlaps the hollow cylinder 46 of the adjusting piston 40. Consequently, there is provided a long peripheral gap 67, which enables a good seal to be effected between the supply bore 32 and the return bore 36. Furthermore, an O-ring seal 70, which in the illustrated nonoperating position provides an effective sealing action, is fitted between a bottom surface 68 of the regulating piston and an inclined end-face 69 of the adjusting piston 40.

The closing piston 42 follows the movement of the regulating piston 41 since, through a stop 71, it is pressed against a resilient sealing washer 74 by a drive spring 72, a disc 73 being interposed. This sealing washer prevents liquid from passing between the chambers 43 and 56 by circumventing the restrictors 59, 60, but permits slight relative movement between the regulating piston 41 an the closure piston 42.

The cutoff valve 39 is formed by the end-face 75 of the closure member 51 and an O-ring seal 76, the end position being defined by the end-face 77 of the insert. The O-ring 76 lies in a groove 78 of considerably greater diameter. It is guided on a securing pin 79 which is inserted in a bore in the insert 36.

When the pump 1 IS started and the pump pressure rises, the

adjusting piston 40 is first pushed downwardly, while the regulating piston 41 maintains its nonoperating position. After a certain period of time, the restrictor 59, 60 opens and oil under pressure passes into the chamber 56. Consequently, the regulating piston 41 also moves into a position determined by the pressure drop at the restrictor. This movement is followed by the closure piston 42 under the action of the drive spring 72. In this way the size of the restrictor 59, 61) is corrected. A stable operating condition is established. The regulating piston 41 is enabled rapidly to follow smaller fluctuations in pressure, since it is loaded at both ends by liquid having only a small difference in pressure, and the spring 64 can also be relatively weak. Greater fluctuations in pressure however can also have a reaction on the constrictor by way of the sealing piston 42. If however the overall pressure-level of the pump changes, the adjusting piston 40 and therefore the restrictor are displaced, so that completely new conditions of equilibrium result.

If the pump is now switched off, the pressure in the chamber 43 drops and the rated spring 44 pushes the adjusting piston upwardly. As this takes place at considerable speed, the oil in the bottom chamber 61 acts as a transmission element, so that the closure piston 42 is driven along and the closure member 51 is pressed on to the seat of the cutofi valve 39.

If the oil delivered by the pump contains air, and the oil reaches the chamber 56, there would have occurred, in the past, the danger of this air flowing away preferentially into the return pipe 8 by way of the throttle point formed between the end-edge 65 at the mouth 33. The reduction of volume in the chamber 56 leads to a corresponding reduction in pressure which causes the regulating piston 41 to slide upwardly and therefore causes the cutoff valve to close. If however as provided for by the invention, a higher pressure obtains in the return pipe 8, the compressed air in the chamber 56 is discharged considerably more slowly through the return pipe 8, so that the above-described danger cannot arise. The same also applies in the case of differently constructed combined pressure-regulating and cutoff valves.

We claim:

1. A pump assembly comprising, a gear pump of the type which forms a group of expanding inlet chambers and a group of contracting outlet chambers on opposite sides thereof, said pump having a predetermined delivery pressure, inlet and out let means for said pump, a pressure regulator having an inlet connected to said pump outlet, said regulator having a main outlet and a bypass return outlet, liquid feed means between said groups of expanding and contracting chambers in the region of greatest chamber volume, said liquid feeding means supplying said chambers in the region of greatest chamber volume with a liquid from said pressure regulator having a pressure between atmospheric pressure and said delivery pressure, a return pipe for returning liquid to a sump connected to said regulator bypass return outlet, valve means in said return pipe openable at a pressure substantially equal to said liquid pressure, conduit means on the upstream side of said valve means extending from said return pipe to said liquid feeding means, said valve means having throttle means extending from the upstream side thereof to the downstream side thereof, said throttle means presenting a greater resistance to pressurized liquid than to pressurized air.

2. A pump assembly according to claim 1 wherein said valve means includes a valve seat member and a closure member having engageable surfaces, said throttle means being a groove in one of said engaging surfaces. 

1. A pump assembly comprising, a gear pump of the type which forms a group of expanding inlet chambers and a group of contracting outlet chambers on opposite sides thereof, said pump having a predetermined delivery pressure, inlet and outlet means for said pump, a pressure regulator having an inlet connected to said pump outlet, said regulator having a main outlet and a bypass return outlet, liquid feed means between said groups of expanding and contracting chambers in the region of greatest chamber volume, said liquid feeding means supplying said chambers in the region of greatest chamber volume with a liquid from said pressure regulator having a pressure between atmospheric pressure and said delivery pressure, a return pipe for returning liquid to a sump connected to said regulator bypass return outlet, valve means in said return pipe openable at a pressure substantially equal to said liquid pressure, conduit means on the upstream side of said valve means extending from said return pipe to said liquid feeding means, said valve means having throttle means extending from the upstream side thereof to the downstream side thereof, said throttle means presenting a greater resistance to pressurized liquid than to pressurized air.
 2. A pump assembly according to claim 1 wherein said valve means includes a valve seat member and a closure member having engageable surfaces, said throttle means being a groove in one of said engaging surfaces. 